Comparing Sectional and Total Dentin Bond Strengths of Three Endodontic Sealers after Using the Single-cone Obturation Technique: An In Vitro Study

INTRODUCTION

The success of endodontic treatment depends on the effectiveness of chemo-mechanical preparation and tight-seal obturation, which is essential to prevent canal infection and apical microleakage. Despite the effectiveness of contemporary obturation techniques, they cannot provide a full fluid-tight seal, require a significant amount of time, and require specialized equipment.¹ The popularity of the single-cone obturation technique can be attributed to the widespread availability of nickel–titanium (NiTi) rotary files and the corresponding gutta-percha cones.²

The choice of root canal sealer plays a significant role in the success of any obturation technique, particularly the single-cone technique.³ The chemical composition of these sealers can influence their root canal sealing ability, affecting the overall success of the root canal filling procedure.⁴ Consequently, the development of high-quality endodontic sealers is essential to minimize at least microbial leakage after endodontic treatment.

AH Plus (Dentsply DeTrey GmbH, Konstanz, Germany) is an epoxy resin-based sealer that has excellent physicochemical properties and apical sealing ability; making it a popular choice for comparative studies.⁵ RealSeal SE (SybronEndo, Orange, CA, USA) is a fourth-generation dual-cure self-etch methacrylate resin-based sealer that eliminates the need for separate etching and bonding steps, thus reducing the risk of errors.⁶ RealSeal SE chemically bonds to radicular dentin and polymer-based core material such as Resilon (SybronEndo, Orange, CA, USA), creating a monoblock effect that enhances canal sealing and root strength.⁷ Silicone-based sealers are also known for their superior sealing capabilities due to their setting expansion, insolubility, and flowability.⁸ The GuttaFlow 2 (Coltène/Whaledent, Langenau, Germany), introduced in 2012 as a substitute for GuttaFlow, is a silicon-based sealer that includes gutta-percha powder, and nano-silver particles with a solubility of 0%, slight setting expansion, good flow and good adhesion to dentin.⁹ Thus, it is recommended for the single-cone gutta-percha obturation technique.⁹ However, dental professionals could face challenges in understanding how the composition of sealers affects their bond strength to radicular dentin, which could impact the success of endodontic treatment. The quality of bonding between endodontic sealers and radicular dentin is critical to maintaining the integrity of the root canal seal. The push-out test is a commonly used method to evaluate this bond strength.¹⁰ Therefore, using this test to assess the performance of root canal sealers in the single-cone obturation technique could provide valuable information to make informed decisions that lead to better long-term clinical outcomes.

This study aimed to evaluate the dentine bond strength of three different endodontic sealers used with the single-cone obturation technique: Epoxy-based resin, methacrylate resin, and silicon/gutta-percha powder-based sealers. Essentially, this study seeks to determine whether variations in sealer chemical composition result in significant differences in dentin bond strength values.

The null hypothesis of the study suggested that there were no significant differences between the total and sectional bond strengths of the experimental sealers. The practical implications of these findings could guide dental professionals in choosing the most appropriate sealers, potentially leading to more effective obturation procedures.

MATERIALS AND METHODS

RESULTS

Table 2 displays total and sectional push-out bond strengths (MPa) for all groups. The one-way ANOVA test revealed significant differences in total bond strengths between the groups (p < 0.05). The third group (RealSeal SE) had the highest total bond strength (21.56 MPa), which was not significantly different from the first group (AH Plus Jet, 17.72 MPa), but was significantly higher than the second group (GuttaFlow 2, 14.19 MPa).

In terms of coronal bond strength, the first group (AH Plus Jet) demonstrated significantly a higher mean value (19.85 MPa) compared to the second and third groups (14.35 MPa and 13.61 MPa, respectively). The third group (RealSeal SE) showed significantly higher mean values of middle and apical bond strength (23.47 and 24.59 MPa, respectively) compared to other groups. The apical bond strengths in all groups were significantly higher than the middle and coronal bond strengths, except for the first group, which had superior coronal bond strength. No significant differences were observed between the apical and coronal bond strengths in the first group.

Table 3 presents the distribution of failure modes, with the first and second groups predominantly experiencing cohesive failure (90%), while adhesive failure was more common in the third group (53.3%). Cohesive failure was also significant in the third group (40%).

The SEM examination showed variable gaps and seals at the sealer-dentin-core interfaces (Figs 3 to 5). AH Plus sealer showed better adaptation with the dentinal walls and core materials in the coronal root sections compared to the apical and middle root sections (Fig. 3). Conversely, GuttaFlow 2 exhibited a higher incidence of gaps at core-sealer and dentin-sealer interfaces, with these gaps predominantly occurring at the core-sealer interface, particularly in the coronal and middle root thirds (Fig. 4). However, GuttaFlow 2 showed better adaptation to dentin and core in the apical root section. The RealSeal SE showed poor adaptation to core material especially in coronal root sections, where there was a good adaptation with the dentin and core material in the apical and middle root sections (Fig. 5). Additionally, RealSeal SE achieved a deeper penetration into dentinal tubules in all root levels than GuttaFlow 2 and AH Plus Jet.

DISCUSSION

This study aimed to compare the total and sectional bond strength of three endodontic sealers (AH Plus Jet, GuttaFlow 2, and RealSeal SE) with radicular dentin when using the single-cone obturation technique. The results showed significant differences in bond strength values among the tested sealers, therefore the null hypothesis was rejected.

The correction factor recommended by Chen et al.¹¹ was applied during bond strength calculations. This adjustment was necessary due to the significantly lower modulus elasticity of Resilon (86.58 MPa) and gutta-percha (100 MPa) compared to dentin (16,000 MPa).^12,13 The thickness of each root section was consistent with the guideline provided by Chen et al.,¹¹ who commended a thickness greater than 60% of the filled canal diameter to ensure no impact on the push-out bond strength. The thickness of all root sections was 1 mm, with canal diameters ranging from 0.5 to 1.16 mm. The plunger tips were intentionally sized about 0.85 times smaller than the canal diameter to avoid contact with the root dentin during the test.^14,15

RealSeal SE and AH Plus Jet demonstrated significantly higher total push-out bond strength values compared to GuttaFlow 2. The reduced bond strength of GuttaFlow 2 could be attributed to the presence of tiny voids resulting from a high sealer-to-gutta-percha ratio in the single-cone obturation technique and lower contact angles affecting its dentin wettability due to the presence of silicon oil in its composition.^16,17 This finding agrees with Bhandi’s findings.¹⁸

Regarding sectional bond strength, significant differences were observed among the sealers tested, consistent with Carneiro et al.¹⁹ Generally, bond strength values were greater in the apical root sections, except for AH Plus Jet, which showed superior bond strength in the coronal region. This could be related to the presence of larger coronal dentinal tubules.¹⁹ RealSeal SE outperformed both in the middle and apical sections, congruent with Pawińska et al.²⁰ and Skidmore et al.,²¹ but in contrast to Chandarani et al.²² This discrepancy might be due to the methodologies used. Furthermore, RealSeal SE exhibited stronger bonding to the middle and apical radicular dentin than the coronal region. This difference can be attributed to the higher density of dentinal tubules in these areas and the slower setting time of the sealer.^23,24 The weaker bond strength of RealSeal SE in coronal radicular dentin could be linked to polymerization shrinkage during coronal photopolymerization.¹⁴

GuttaFlow 2 demonstrated apical bond strength comparable to AH Plus Jet and RealSeal SE, in line with Bouillaguet et al.²⁵ This similarity can be attributed to the low viscosity, pseudoplasticity, and setting expansion of GuttaFlow 2.²⁶ However, these results contrast with the findings of Adhikari and Jain,²⁶ which favored GuttaFlow in apical adaptation. In the middle root sections, GuttaFlow 2 and AH Plus Jet showed comparable bond strengths, though lower than RealSeal SE. In the coronal region, GuttaFlow 2 and RealSeal SE displayed similar results, which were significantly lower bond strengths than AH Plus Jet, likely due to the suboptimal adaptation of GuttaFlow 2.²⁴

Cohesive failure modes were predominant in both AH Plus Jet and GuttaFlow 2, indicating their superior bonding to dentin compared to Gutta-percha in the single-cone obturation technique.²⁷ RealSeal SE showed high percentages of adhesive and cohesive failure modes, which is consistent with the findings of Carneiro et al.¹⁹ The cohesive failure mode of AH Plus Jet may be attributed to its stronger bond to both dentin and gutta-percha.²⁸ The cohesive failure of GuttaFlow 2 might be due to better adhesion to dentin than gutta-percha, supported by the study’s results.

Scanning electron microscope evaluations revealed that AH Plus Jet adapted excellently to dentin walls but with shallow penetration into dentinal tubules and multiple tiny gaps at the sealer-core interface. GuttaFlow 2 displayed numerous wide gaps at the sealer-dentin and sealer-core interfaces, along with large voids within the sealers. RealSeal SE, on the other hand, exhibited excellent adaptation to dentin walls with deeper penetration into the dentinal tubules. These findings were consistent with Jain and Adhikari and supported by the current results of the push-out test.²⁹ The penetration of sealer into the dentinal tubules enhances radicular sealing by increasing the contact areas between dentin and filling materials. However, some authors suggested that the force required to dislodge the filling materials from the root canals is independent of the depth penetration of sealer into dentinal tubules.³⁰ Based on the results of this study, it is recommended to use the RealSeal SE obturation system when the post and core restoration is planned, as this system had the highest bond strength in the apical and middle root sections.

Although informative, this study has some inherent limitations, such as variations in moisture levels within dentinal tubules, the lack of strict standardization in sealer application, and a focus that does not encompass voids within the sealers. The absence of SEM analysis on samples following the push-out test could be seen as a limitation, as this analysis could provide valuable insights into the failure mode. Future research should also explore innovative techniques and materials aimed at minimizing potential void formation within sealers and enhancing their adaptability in different regions of the root canal. Additionally, investigating the influence of variables such as sealer application volume and moisture control on bond strength could further contribute to improving the clinical performance of endodontic sealers.

CONCLUSION

Within the limitations of the current study, the overall bond strength of RealSeal SE and AH Plus Jet outperformed GuttaFlow 2 when the single-cone obturation technique was used. However, Realseal SE exhibited superior bond strength in the apical and middle root thirds, while AH Plus Jet had the greatest bond strength in the coronal root thirds.

ACKNOWLEDGMENT

The author would like to thank Ajman University, UAE for its support during this study.

AUTHOR CONTRIBUTIONS

Mohamed Elsayed (author) designed the work and critically reviewed the manuscript and approved the final version, performed the laboratory work, analyzed the data, and critically reviewed the manuscript. The author approved the final manuscript and is accountable for all aspects of the work, in ensuring questions related to the accuracy or integrity of any parts of the work are appropriately investigated and resolved. The author has read and agreed to the published version of the manuscript.

DATA AVAILABILITY STATEMENT

The data used to support the findings of this study will be available from Dr Mohamed Elsayed at this email: elsayednada@yahoo.com for the researchers who meet the criteria for accessing this data. The data can be requested after the publication of this article. However, requests for the data, [6/12 months] after the publication of this article, will be considered by the corresponding authors.

ETHICS

Local Research Ethics Committee (RD-2014/15-23).

ORCID

Mohamed El Sayed https://orcid.org/0000-0003-3391-5306

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